1. Field of the Invention
My invention is in the field of heating, ventilating and air-conditioning (cooling) systems.
In particular it relates to central systems for heating, ventilating and cooling buildings having multiple independently managed area modules, among which it is desired to apportion equitably the cost of heating, ventilating and cooling. Typical of buildings having such a requirement are shopping centers incorporating a great variety of types and sizes of business activity, frequently with public areas used in common by all of the businesses, and office buildings, condominia, and apartment buildings utilizing common air-distribution systems.
2. Prior Art
In the past where multiple independent activities have been served by a common cooling or heating unit, problems have arisen as to fairness of apportionment of the cost of operating the unit. Some tenants may wish to keep their areas at a very different temperature than others. Some tenants may have a much greater "heat load" due to people in their areas, or due to high lighting levels, cooking equipment, or other sources which transfer heat to the air in the area. Some tenants may wish to keep large doors in their areas open to the outside, so that significant amounts of the heated or cooled air from the central distribution unit never reach the return duct, and are simply wasted to the out-of-doors.
Formulas for apportioning the cost of operating a cooling or heating unit based on square footage of an area module, or based on number of employees or gross sales or store frontage, obviously will all fail of fairness, because the causes of cooling or heating demand variation described in the previous paragraph are almost completely independent of such arbitrary formulas.
Many designers of large multiple-occupancy buildings, facing this bewildering array of variables, have simply thrown up their hands and provided each tenant with a separate air conditioner and/or heater, so that each tenant controls and pays for his own cooling or heating costs directly. However, this solution to the problem is a poor one for several reasons: (1) the separate units are more costly at purchase than a shared system; (2) most area modules are provided with much larger machines than necessary, since they are selected to accommodate the most extreme demands contemplated for the area module without regard to the type of tenancy; (3) commercial availability of the individual units is subject to considerable fluctuation, often delaying completion of construction; (4) structural mounting provisions for the individual units increase the cost of construction, in comparison with ducting from a central unti; and (5) overall cost of operation, after installation is complete, is higher for the combined individual units than for a common central system.
In installations using radiative heating or cooling systems in which chilled or heated water is circulated through heat exchangers in each area module, designers have attacked the problem by providing meters to monitor the flow and change in temperature of the water passing through each heat exchanger and utilizing these data to prorate the cost of operating the central system. An example of such a system is the ITT Barton "Model 950 BTU Computer," with "Model 392 Electronic Temperature Transmitter" and "series 7000 Turbine Meters." These components are described in Barton's Product Bulletins number 950-1, 392-4 and 7000-5, respectively. This technique cannot be used with variable-volume air distribution systems, since there is no way to measure the increase or decrease in temperature of the air entering each module, or the extent to which a given volume of air effects the temperature within the module. Furthermore, even as it is used in connection with radiative heating and cooling systems, this method is intrinsically inequitable, since it only gives the appearance of prorating the total operating cost on the basis of the energy used by each tenant. The various well known factors which adversely influence the efficiency of radiative heat exchangers make the comparison of heat gained or lost through the tenants' radiators practically meaningless.